Manchester United fans ignored the request of manager Alex Ferguson by taunting bitter rivals Liverpool during a 4-0 Premier League victory over Wigan at Old Trafford on Saturday.
Ferguson takes his team to Anfield next weekend for the first Liverpool home game since the findings of an independent panel investigating the Hillsborough disaster were published this week.
The panel's report cleared Liverpool fans of any wrong-doing in the tragedy that cost the lives of 96 of their supporters at the 1989 FA Cup semi-final at the Hillsborough ground in Sheffield, northern England.
Ferguson said on Friday he hoped both sets of supporters would "draw a line in the sand" in their heated rivalry, which has featured United fans taunting Liverpool over Hillsborough while some Liverpool followers have mocked the 1958 Munich air crash which claimed the lives of eight United players.
However, minutes into the Wigan game, large sections of United fans were chanting anti-Liverpool songs, one of which included the refrain: "It's never your fault. You're always the victims, it's never your fault."
United fans took to social media later to claim that chant was specifically directed at Liverpool striker Luis Suarez and his much-publicised race row with United defender Patrice Evra last season.
However, the timing of the fans' response, days after the Hillsborough report was published, made such an excuse ring hollow.
Even ignoring the tastelessness of their actions, the singing also marked a stunning disregard of Ferguson's wishes, a point confirmed in a club statement issued after Saturday's match.
A United spokesperson said of Saturday's chants: "The club deplores it.
"The manager has made the club's position very clear on this matter, it's now up to the fans to respect that."
Ferguson was forthright when talking about the behaviour he expects from United fans next week.
"I think what will happen for that Liverpool game, I think there is such a focus on it at the moment, fans will be on their best behaviour," he said Friday.
"I think it's a moment for those two great clubs to show why they're two great clubs. I don't anticipate any problems.
"There are always opportunities to show your greatness and I think this is another one."